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³²P Distribution in Oligonucleotides of 28 S Ribosomal RNA of the Novikoff Hepatoma and Normal Rat Liver¹

Department of Pharmacology, Tumor By-Products Laboratory, Baylor College of Medicine, Houston, Texas 77025

Previous studies from this laboratory have indicated that the ³²P nucleotide composition of nucleolar 45 S, 35 S, and 28 S RNA of tumors is characterized by a lower adenylic acid content and a higher cytidylic acid content than that of nontumor tissues (3). In addition, it was found that the isotope content of the dinucleotides GC and GU of hepatomas was significantly higher than that of normal liver (18). For determination of whether these differences represented isotope effects or segmental differences in these large molecules, studies were made on other dinucleotides, as well as studies of longer segments of these molecules. The isotope content of the dinucleotides AC and AU were not significantly different in hepatomas and normal liver (18). The present study shows that in the B₃ fragment (which is 600 nucleotides long) of the Novikoff hepatoma and in normal liver there are no significant differences in ³²P nucleotide composition or in isotope content of the oligonucleotides. Accordingly, the differences found in nucleolar RNA's of tumors and other tissues represent segmental differences in these molecules, rather than isotope effects.

¹ This work was supported in part by Cancer Research Center Grant CA-10893, American Cancer Society Grant P-339, and Cancer Training Grant CA-05154.

² Postdoctoral trainee of the National Cancer Institute.

Received 6/ 2/69. Accepted 8/ 7/69.